Method for restricting fluid pathways through a subterranean formation zone

ABSTRACT

This invention resides in a method for restricting fluid pathways through a subterranean formation zone. A polymerizable material capable of forming popcorn polymer is positioned in the formation zone, maintained under polymerization conditions for a time sufficient to polymerize in situ at least a portion of the material and restrict fluid pathways through the zone without exerting a force on the formation which is of greater magnitude than the magnitude required for fracturing the formation zone.

United States Patent [191 Buce [111 3,771,599 Nov. 13, 1973 METHOD FORRESTRICTING FLUID PATHWAYS THROUGH A SUBTERRANEAN FORMATION ZONE [75]Inventor: Walter F. Buce, Bartlesville, Okla.

[73] Assignee: Phillips Petroleum Company,

Bartlesville, Okla.

[22] Filed: July 18, 1972 [2]] Appl. No.: 272,963

[52] U.S. Cl. 166/295, 175/72 [51] Int. Cl..., E21b 33/138 [58] Field ofSearch 166/295, 294, 270,

[56] References Cited UNITED STATES PATENTS 3,608,639 9/1971 Hart166/295 3,158,210 11/1964 Cannon et a1. 175/72 3,448,800 6/1969 Parkeret a1. 175/72 X 3,467,208 9/1969 Kelly, Jr 175/72 3,568,782 3/1971 Cox175/72 3,150,726 9/1964 Bodine 166/295 X 3,251,414 5/1966 Willman..... I166/295 3,379,253 4/1968 Chism 166/295 3,412,796 11/1968 Dekking 166/2953,603,397 9/1971 Peray 166/295 X 3,637,019 l/l972 Lee 166/295 PrimaryExaminer-Stephen J. Novosad Attorney-James W. Williams et a1.

[57] ABSTRACT 10 Claims, No Drawings METHOD FOR RESTRICTING FLUIDPATHWAYS THROUGH A SUBTERRANEAN FORMATION ZONE This invention resides ina method for restricting fluid pathways through a formation. Apolymerizable material capable of forming hard, porous, relativelyinsoluble popcorn polymer is placed in the formation and theremaintained under polymerization conditions for a time sufficient topolymerize in situ at least a portion of the material and restrict fluidpathways through the zone without exerting a force on the formation zoneof a magnitude sufficient for fracturing the formation zone.

Heretofore methods of preventing lost circulation in a formation zoneduring drilling operations, for example, involve pumping losscirculation material into the zone. These materials were wedged into thepores and indices of the formation with fluid pressure. In largepathways, these methods were often unsuccessful owing to the fact thatthe material could not be maintained at their desired location. Variouspolymers have been found which can be polymerized in situ for reducingthe fluid pathways. These heretofore utilized polymers sometimes failedowing to the fact that portions of the polymer plug would be washed fromtheir locus by the high formation pressure and movement of the thevariables of the formation physical properties, characteristics,temperatures, pressures, and the fluids contained therein. Once theseconditions are known by analysis as heretofore described, one skilled inthe art can easily determine the popcorn polymer growth that is desiredunder the in situ conditions for maintaining the forces exerted by thepolymer below the magnitude of the forces which will fracture theformation.

Popcorn polymer is sometimes referred to as cauliflower, sponge, andKondakos. Popcorn polymer is a hard, porous opaque material that is notsoluble in ordinary solvents. The occurrence of popcorn polymer is wellknown in chemical plants such as for example a synthetic rubber plantand as described in Industrial polymer portion by fluids passing undersometimes high volocity passing in contact with the polymer. Where thevoid desired to be restricted or sealed is large relative to the poresof the formation, for example vuggy formations, fractured strata, orcavernous carbonaceous materials, the problem of effectively restrictingfluid flow through zones of the formation is made exceedingly moredifficult.

By the method of this invention, a polymerizable material capable offorming hard, porous relatively insoluble popcorn polymers is placed inthe formation zone desired to be sealed. The material is theremaintained under polymerization conditions for a time sufficient topolymerize in situ at least a portion of the material and restrict fluidpathways through the zone without exerting a force on the formation zoneof a magnitude sufficient for fracturing the formation zone.

As known in the art, the amount of material utilized is a function ofthe physical properties of the formation zone and the radial extent fromthe well bore that is desired to be sealed. These variables areroutinely calculated by one skilled in the art from data of theformation zone such as core analysis, well logs, and other analyticalmethods and procedures.

Although the instant invention is primarily directed to sealing orrestricting the fluid pathways through a subterranean formation zoneadjacent a well bore, it should be understood that this invention can beutilized in other conditions and situations.

Where the zone desired to be sealed is adjacent a well bore, thepolymerizable material is pumped from the surface downwardly through thewell bore and outwardly through the formation from the well bore. Any ofthe many procedures for selectively positioning the material in thedesired zone can be utilized such as, for example, straddle packers,etc.

The time necessary for polymerizing a preselected concentration of thepolymerizable material to restrict the fluid pathways without exerting aforce on the formation zone of a magnitude sufficient for fracturing thematrix of the formation zone is also dependent upon and EngineeringChemistry, July, 1947, page 830, inhibition of Polymerization,Laboratory and Plant Control of Popcorn Polymer Growth by M. S. Kharaschet al.

Although the formation of popcorn polymer particles or seeds is arelatively slow process, it has been discovered that polymer growth froman existing seed is a very rapid reaction. Therefore it is preferredthat popcorn polymer particles or seeds be placed within the formationin order to provide growth with resultant sealing. Regardless of themethod of initiating polymer growth within the formation, by formingseeds therein or by initially placing seeds within the formation incontact with monomers, the most remarkable characteristic is thephenomenon of growth which a seed exhibits when in contact with liquidor gaseous monomers. It has also been discovered that when butadiene,styrene, or a mixture of the two, for example, is brought into contactwith a popcorn polymer seed, the bulk of the monomers is rapidlyconverted into a popcorn polymer that is similar in properties to theoriginal seed. Since most all American syntheti'c-rubber-manufacturingplants, for example, have active popcorn polymer seeds in the operatingequipment, it is therefore more convenient and less time consuming topractice the method of this invention by utilizing popcorn polymer seedsas opposed to first producing seeds within the formation and thereafterpromoting popcorn polymer growth to produce the desired forces on theformation.

Popcorn polymer growth is somewhat proportional to the peroxide content.For this reason whenever the polymer growth is continued without theaddition of new peroxide groups, subsequent growth is less active thanpreceding growth. It then sometimes becomes necessary to supplyadditional peroxide groups such as, for example, hydroperoxides, to thepolymerizable material within the formation. This is especially truewhen the voids to be sealedare relatively large.These groups are mostreadily formed when oxygen attacks methylene groups adjacent aliphaticdouble bonds. Consequently, the more methylene groups present in thepolymerizable material within the formation, the greater will be therate and resultant growth of the popcorn polymer therein. Examples ofmaterials containing such methylene groups are polybutadiene, copolymerscontaining considerable butadiene, and others known in the art. Popcornpolymer seeds are known to grow rapidly in not only styrene, butadiene,or mixtures thereof but also in other unsaturated monomers such as, forexample, isoprene, methyl-methacrylate.

' Since pressure and temperature conditions of various formations varywidely relative to one another and the growth rate of popcorn polymersvaries among the EXAMPLE I Formation Depth 5500 feet FormationTemperature 185F. Formation Pressure 7 2106751:

Formation Type in Place Fluid Polymerizable Fluid Vugged limestone,broken Brine (10 lbs/gal) Butadiene butadiene opcom polymer seeds Volume500 Gallons 10 pounds powdered seeds Distance extending from Well Bore10 feet Flush Medium Utilized Crude oil Initial Formation Face Pressure1 10 psi After polymerization conditions are maintained for 12 hours thezone of loss circulation is sufficiently sealed to permit continueddrilling operations at previously used mud pressures and experiencingnormal fluid loss.

It is preferred that in situ polymerized popcorn polymer form a volumeof polymer not substantially greater than the total effective porosityof the zone portion desired to be restricted. This will assure sealingof the zone without fracturing the formation which might cause furtherlost circulation.

In order to further assure sealing of the zone, lost circulationmaterial, as known in the art such as natural and synthetic fibers ormaterials, can be incorporated in the polymer material subsequent topolymerization thereof. Upon polymerization of the polymer, thesefibrous materials will be forcibly urged into indices of the matrix andheld firmly at these positions by the formed polymer. Further, thesefibers are generally compressible which will aid in preventingfracturing pressure forces from being exerted on the formation duringpolymer growth.

Where the formation to be sealed is cavernous, badly broken, or containsrelatively large fractures, lost circulation material mixed withadditional polymerizable polymer can be injected into the zone afterpolymerization of the popcorn polymer therein. This procedure isrecommended where large void areas receive the polymer and relativelysmall fractures are passing fluid after the popcorn is formed. The inplace polymer will thus direct the subsequent polymer-fibers to the yetunsealed portions. These subsequent treatments are generally utilizedwhere a complete, absolute seal is necessary.

Other modifications and alterations of this invention will becomeapparent to those skilled in the art from the foregoing discussion andexample, and it should be understood that this invention is not to beunduly limited thereto.

What is claimed is: 1. A method for restricting fluid pathways through asubterranean formation zone, comprising:

placing in the zone a polymerizable material capable of forming hard,porous, relatively insoluble popcorn polymer; and

maintaining said material under polymerzation conditions within theformation for a time sufficient to polymerize in situ at least a portionof the material and restrict fluid pathways through the zone withoutexerting a force on the zone of a magnitude sufficient for fracturingsaid zone.

2. A method, as set forth in claim 1, wherein the polymerizable materialcomprises butadiene.

3. A method, as set forth in claim 1, wherein the polymerizable materialcomprises a butadiene and styrene mixture.

4. A method, as set forth in claim 1, wherein the polymerizable materialis placed in the formation by passing said material downwardly through awell bore and outwardly through the formation.

5. A method, as set forth in claim 1, wherein the polymerizable materialis maintained under polymerization conditions for a time sufficient toform a volume of popcorn polymer substantially not greater than thetotal effective porosity pore space of the zone portion desired to berestricted.

6. A method, as set forth in claim 1, wherein the polymerizable materialis polymerized in caverns of the subterranean zone.

7. A method, as set forth in claim 1, wherein the polymerizable materialis polymerized in fractures of the subterranean zone.

8. A method, as set forth in claim 1, wherein the polymerizable materialhas popcorn polymer particles mixed therewith, said particles beinginsoluble in the polymerizable material, characterized by swelling uponexposure to the polymerizable material and comprising a relatively largenumber of methylene groups.

9. A method, as set forth in claim 1, including mixing lost circulationmaterials with the polymerizable material.

10. A method, as set forth in claim 9, wherein the lost circulationmaterials are one of natural fibers, synthetic fibers, natural fibrousmaterials, synthetic fibrous materials, or mixtures thereof.

2. A method, as set forth in claim 1, wherein the polymerizable materialcomprises butadiene.
 3. A method, as set forth in claim 1, wherein thepolymerizable material comprises a butadiene and styrene mixture.
 4. Amethod, as set forth in claim 1, wherein the polymerizable material isplaced in the formation by passing said material downwardly Through awell bore and outwardly through the formation.
 5. A method, as set forthin claim 1, wherein the polymerizable material is maintained underpolymerization conditions for a time sufficient to form a volume ofpopcorn polymer substantially not greater than the total effectiveporosity pore space of the zone portion desired to be restricted.
 6. Amethod, as set forth in claim 1, wherein the polymerizable material ispolymerized in caverns of the subterranean zone.
 7. A method, as setforth in claim 1, wherein the polymerizable material is polymerized infractures of the subterranean zone.
 8. A method, as set forth in claim1, wherein the polymerizable material has popcorn polymer particlesmixed therewith, said particles being insoluble in the polymerizablematerial, characterized by swelling upon exposure to the polymerizablematerial and comprising a relatively large number of methylene groups.9. A method, as set forth in claim 1, including mixing lost circulationmaterials with the polymerizable material.
 10. A method, as set forth inclaim 9, wherein the lost circulation materials are one of naturalfibers, synthetic fibers, natural fibrous materials, synthetic fibrousmaterials, or mixtures thereof.